96 F. A. HOLTON AND D. D. TYLER 



his findings. In particular, we have repeated Packer's important observa- 

 tion that the phosphorylating, close-coupled heart mitochondrion may be 

 made to alternate between a stable expanded condition and a stable con- 

 tracted condition according to the state of the respiratory chain (expanded 



477-5 m/t 



Time, sec 



Fig. I. Establishment of a stable expanded condition of mitochondria in 

 response to phosphate and succinate. 



Extinction changes at 434 m/^t and at 477 • 5 m/x were measured simultaneously 

 by the method of Holton [10] using a rectangular glass cell with clear walls, sur- 

 rounded on three sides with polished metal plates and maintained at a constant 

 temperature of 18 -8'. Rat heart mitochondria (sarcosomes) were isolated as 

 described previously [11] and were diluted from time o into a medium containing 

 0-28 M sucrose, o-oi M disodium potassium ethylenediaminetetraacetate, pH 7-4, 

 to give 50 ml. of a reaction mixture containing 0-51 mg. biuret protein per ml. At 

 time 177 sec. the optical recording was interrupted and 0-5 ml. of 0-5 M potassium 

 phosphate buffer, pH 7 -4, was rapidly stirred into the suspension. At time 210 sec. 

 0-5 ml. of 0-4 M potassium succinate, pH 7-4, was added in a similar way. Final 

 concentrations were: phosphate, 4-9 mvi ; succinate, 3-9 mM. 



Measurements of the rates of change of extinction observed at the two wave- 

 lengths studied yielded the ratios of rates given in Table I. These values show 

 reasonable agreement with the ratio calculated from Rayleigh's law of light-scatter- 

 ing. This constitutes evidence that the progressive changes of extinction illustrated 

 above were caused by changes in the light-scattering properties of the mitochondria. 



condition with external nucleotide as ATP, respiratory chain in state 4; 

 contracted condition with external nucleotide as ADP, respiratory chain 

 in state 3, following the nomenclature of Chance and Williams [4]). 



More recently we have attempted to answer by experiment two 

 questions concerning the establishment of stable structural states in these 



